Phase-change materials (PCM) are capable of transforming from a crystalline phase to an amorphous phase and vice versa. These two solid phases exhibit differences in electrical properties, and semiconductor devices can advantageously exploit these differences. Given the ever-increasing reliance on radio frequency (RF) communication, there is particular need for RF switching devices to exploit phase-change materials. However, the capability of phase-change materials for phase transformation depends heavily on how they are exposed to thermal energy and how they are allowed to release thermal energy. For example, in order to transform into an amorphous state, phase-change materials may need to achieve temperatures of approximately seven hundred degrees Celsius (700° C.) or more, and may need to cool down within hundreds of nanoseconds.
Repetition of such high temperatures can cause annealing and other thermophysical hysteresis effects which detrimentally change the conductivity of PCM over time. Conductivity skew (i.e. undesirable change in resistance) of PCM due to repeated OFF/ON cycling can result in a PCM RF switch having higher insertion losses in the ON state. Thus, conductivity skew of PCM is a figure of merit that can determine the marketability of the RF switch and its suitability for a given application.
Accurately quantifying conductivity skew of PCM can be problematic. Computer simulations cannot accurately predict the conductivity of PCM over an entire lifetime. It might be necessary to perform more than one million OFF/ON cycles before PCM exhibits any detectable conductivity skew. Further, it might be necessary to detect conductivity skew in thousands of PCM RF switches in order to achieve statistically significant results regarding the degree of conductivity skew for a given PCM RF switch design.
Conventional techniques of testing RF switches, for example, by connecting external probes of an automated test equipment (ATE) to one RF switch at a time, have significant time delays that render generating large sets of test data impractical. When resorting to conventional testing in the context of PCM RF switches, time delays associated with generating the required temperatures to crystallize and amorphize the PCM in each individual RF switch additionally impede generating large sets of test data. Conventional means of testing can also introduce problems associated with the impedance of cables or wirebonds, and reduce the accuracy of test data.
Thus, there is need in the art to generate large sets of data for determining and characterizing conductivity skew of PCM in PCM RF switches accurately and rapidly.